Heating, ventilation, and/or air conditioning (HVAC) systems are often used to control the comfort level within a building or other structure. Such HVAC systems typically include an HVAC controller that controls various HVAC components of the HVAC system in order to affect and/or control one or more environmental conditions within the building. Over time, the HVAC system may begin to operate less efficiently. Diagnosing the cause of the loss in system efficiency may be difficult. Diagnostics may be employed to assist in monitoring the performance of an HVAC system over time.